Control system for electric-steam generators



Oct. 25, 1949. .c. F. BIRCHLER EIAL 2,485,999

' CONTROL SYTEM FOR ELECTRICSTEAM GENERATORS Filed March 4, 1947 2Sheets-Sheet 1 as 32/ 2 J 55 /33A J r L FEED INVENTORS AND CHARLES EBIRCHLER HARRY E. WEAVER BLEED Oct, 25, 1949.

C. F. BIRCHLER ETAL CONTROL SYSTEM FOR ELECTRIC-STEAM GENERATORS FiledMarch 4, 1947 2 Sheets-Sheet 2 51.0w DOWN FIG. 2 v

38 L., 3.5 w.| ,35 W.F.

mmvrozes 9 AND CHARLES F. BIRCHLER 54 HARRY E. WEAVER Patented Oct. 25,1949 CONTROL SYSTEM FOR ELECTRIC-STEAM GENERATORS Charles F. Birchler,East Cleveland, and Harry E. Weaver, South Euclid, Ohio, assignors toBailey Meter Company, a corporation of Delaware Application March 4,1947, Serial No. 732,182

38 Claims.

This invention relates to control systems and particularly to method andapparatus adapted to control the operation of a power producingapparatus such as an electrically heated vapor generator.

In certain localities where hydro-power is abundant, the price ofelectricity is low enough to make economical its use in vaporizing waterinto steam for process or heating uses. In the operation of such vaporgenerators problems of control arise which must be solved in order thatthe temperature and pressure of the produced steam will be of uniformoptimum value under existing demand conditions and with full safety tolife and generating apparatus.

It is an object of our invention to provide both method and apparatus ofcontrol for an electrically heated vapor generator.

We have as a further object the provision of a completely automaticcontrol system for such a vapor generator.

Other objects will become evident upon a study of the specification,drawings and claims.

In the drawings:

Fig. 1 is a diagrammatic representation of one preferred embodiment ofour invention applied to an electrically heated steam generator.

Fig. 2 diagrammatically represents a second embodiment of controldirected to somewhat different operating conditions.

Fig. 3 constitutes a modification of Fig. 2.

Referring to the drawing, the particular unit being described and towhich our control is applied, includes a vertically mounted drum orpressure chamber I supported on a base portion 2. Insulated through theupper head of the drum I and suspended therefrom are three electrodes 3,which may be of cast iron or other suitable material. Electrical poweris applied to the electrodes as at 4 external to the drum I.

External to and above the drum I is a dry drum 5 having steam risertubes 6 and dry drum drain tubes 1. Enclosing the electrodes 3 andspaced therefrom is a clover-leaf neutral plate 8. Vertically positionedalong the side of the drum I are the usual water column and gage glassesdiagrammatically shown at 9. The dry drum 5 is provided with the usualsafety valve I0 and with a main steam exit nozzle II. v

Water is fed to the unit through a feed pipe I2 terminating in a feednozzle I3 centrally located in the lowermost portion of the main drum I.To the lower portion of the drum is also connected a blowdown line I4and a bleed line I5.

The terminals 4 are connected through the necessary electrical apparatusto a source of electrical power; the arrangement forming no part of thepresent invention. The problem with which our method and apparatus areconcerned is the supply of water to the unit, the extraction of watertherefrom, the maintenance of desired level of liquid within the drum I,as well as the conductivity of the liquid within the drum; all in properdegree so that the vapor which is generated will satisfy the rate demandwhile maintaining the desired pressure.

In such a vapor generator, the heat for vaporizing the water is suppliedby the passage of electric current through the water itself, from oneelectrode to another or to the neutral plate. Since the voltage of thepower supply is constant, the energy consumed varies directly with thecurrent, while the current varies inversely as the resistance of thepath it travels. The resistance of the path, in turn, depends upon thecross-sectional area of the Water conductor (path) and upon thespecific,

resistance of the water itself. Inasmuch as the electrodes are fixed inposition, the water area through which the current can pass isdetermined by the depth of immersion of the electrodes; i. e. the heightof water Within the boiler drum. The specific resistance of the water isa function of the concentration or amount of dissolved solids in thewater and also of the temperature of the water.

Thus, in a boiler of this type, the amount of steam generated dependsupon the amount of electric current passing through the water and this,in turn, depends upon the area of the path through the water and uponthe conductivity (or resistivity) of the water to the passage ofelectric current therethrough. The water area through which the currentcan pass is determined by the depth of immersion of the electrodes.Therefore,

if we maintain a constant specific resistance of the water, the amountof steam generated may be controlled by varying the level of the waterin the boiler.

Thus in order to maintain a substantially uniform value of steampressure, while satisfying the demand upon the boiler for quantity rateof steam generated, we are confronted with the problem of controllingthe level of liquid within the boiler drum as well as the specificresistance of the water. A variation in any one, or all, of the threevariables, namely, the amount of water within the boiler, itsconcentration of impurities, or its temperature, may cause a desirableor an undesirable variation in steam pressure and/ or rate of steamgeneration.

The water fed to the unit will always contain a certain percentage ofdissolved solids and par ticularly if the greater portion of watersupplied is other than condensate. Inasmuch as the steam does not carryaway salts or solids from the boiler there is a continuous tendency tobuild up the concentration of solids within the boiler water and thusto'continually vary the resistivity to current passage through the waterpath. When operating at rated capacity the boiler hourly evaporatesabout ten times the water normally contained in it. In general, it maybe said that if the conductivity of the water is maintainedsubstantially uniform the rate of steam generation will vary with thewater level. Conversely if the level is maintained substantially uniformthen the rate of steam generation will vary with the concentration ofdissolved salts in the boiler water. In order to keep the concentrationof the water from gradually increasing (.Which would make inaccurate anyfunctional relationship between water level and vapor generation) it isadvisable to continually bleed some part of the highly concentratedwater from the lower portion of the boiler drum in a controlled manner.If this is properly accomplished then a control of level within the drumis a control of rate of steam generation.

The interrelation of the effects of the operating Variables may,however, cause disturbances in the primary control of level or ofconductivity. For example, the conductivity of the water is not only afunction of the amount of dissolved solids therein but is also afunction of the temperature of the water.

By way of example: if there is an increase in demand upon the vaporgenerator the steam pressure will tend to fall. Assuming, for themoment, a uniform conductivity of the water then the increase in demandindicates a desirability of raising the level of water within the boilerand thus increasing the path for electric current and thereby increasingthe rate of current dissipation and consequently the rate of steamgeneration. However a rapid increase in the rate of supply of water willtend to dilute the water within the boiler, thus lowering itsconductivity, and at the same time will tend to cool the water withinthe boiler which also effects a lowering of its conductivity. Both ofthese adverse eflects are opposite in nature to any increase in vaporgeneration desired by increasing the level and thus the area ofconductor path. It is, therefore, apparent that a proper control must bejudicious in regard to varying the level of water and must definitelytake into account such adverse effects as have been mentioned.

. Giving consideration to such disturbing influ ences as have beenmentioned, which are effective principally under conditions of wide andrapid variations in demand, we have found that a somewhat differentarrangement of control is preferable when operating under substantiallysteady load conditions than when operating under rapidly varying loaddemand. The arrangement of Fig. 1 is particularly directed to mostefficient operation of a unit having substantially uniform load demand,although not limited thereto.

The primary functions accomplished by our control system, as depicted inFig. 1, may be summarized as follows:

1. To so control the rate of admission of feed water to the unit as tomaintain a uniform steam pressure, through varying the liquid immersionof the electrodes in relation to steam demand.

2. To so regulate the rate of bleed from the unit that the conductivityof the water remains substantially constant at all levels and rates ofoperation.

3. To prevent abnormal water level conditions by a control of blowdown.

Theoretically, with a constant voltage applied to the electrodes, and auniform conductivity of the boiler water, the rate of steam generationwill vary directly with the amount of immersion of the electrodes, i. e.the level of Water in the boiler. Thus we desire a geared range betweensteam pressure (as an indication of demand upon the boiler) and waterlevel, namely, a definite relation between level and load demand.

Referring now to Fig. 1, it will be seen that a feed water control valveI6 is positioned conjointly responsive to steam pressure and waterlevel, so that as the steam pressure drops, indicating an increasingdemand or steam outflow, the rate of water supplied to the boiler willbe increased in proportion to deviation of steam pressure from thedesired value or standard. Should there be fluctuations in feed waterpressure, the feed water flow will fluctuate accordingly, so that ameasure of water level is used to modify the primary steam pressureeffect so as to maintain the level at a proper value. In effect, thistwo-element control maintains a deflnite water level for a given loaddemand. As steam pressure decreases (indicating increased steam outflow)the rate of water supply will be increased proportionately to thedeviation of steam pressure from standard. The electrodes are subject towearing away or scaling up, with consequent variation in steamgeneration rate per inch of submergence. Steam pressure as an element inthe control of feed water supply has the advantage of correcting forsuch changes in the relationship between level and rate of steam output.

Connected to the steam outflow conduit [1, we show a Bourdon tube [8sensitive to pressure of the steam and arranged to vertically positionthe stem IQ of a pneumatic pilot valve 20, which is adapted to establishin the pipe 2| an air loading pressure bearing a definite relation topressure of the steam in the conduit l1. Such a pilot valve is disclosedand claimed in the patent to Johnson 2,054,464. The loading pressurethus established in the pipe 2| is applied to the A chamber of astandardizing relay 22 which may be of the type disclosed and claimed inthe patent to Gorrie 2,098,914.

Air under pressure is supplied to the relay 22 through reducing valves24 and 25 from a source 23. The reducing valves supply air at selectedreduced pressures to the pipes 26 and 21 in which are located bleedvalves 28 and 29 each having an adjustable bleed orifice to theatmosphere. The pipes 26 and 21, beyond the bleed valves 28, 29 join theinlet and outlet connections of the D chamber of relay 22. By way ofexample, the pressure in the pipe 26, between elements 24 and 28, may be25 p. s. i., while the pressure in the pipe 21 between elements 25 and29 may be 5 p. s. i.

Variations in the loading pressure established by the pilot 20,effective in the chamber A, produce a control pressure in the chamber Dto which is connected the pipe 30. Chamber B is open to the atmospherewhile chamber C is interconnected with chamber D by an adjustable bleedconnection. The result is that for any change in the loading pressureapplied to chamber A, the control pressure in chamber D will beinitially varied in proportional amount with a slow folthe water levelcontroller 35 assumes precedence over the steam pressure controller l8and maintains the water level in the boiler drum within the desiredlimits without regard to steam pressure changes. Thus the boiler isprevented from flooding or from becoming empty.

In order to limit the maximum and minimum values of the control pressureapplied to pipe 30 we limit the maximum air pressure in the pipes 26 and21 through adjustment of the elements 24, 25, 28 and 29. Assuming that amaximum pressure of 25 p. s. i. is available in the pipe 26 through thebleed valve 28 and to the inlet of the chamber D then this is themaximum control pressure which can be applied to the pipe 30 when theinlet valve is open and the outlet valve is closed. Under a reverseextreme condition, when the inlet valve is closed and the outlet valveis open, the elements 25 and 29 are so adjusted that the pressuresWithin the chamber D cannot decrease below a minimum of say p. s. i.

The pipe 30 connects to the B chamber of a differential standardizingrelay 3| for establishing a control pressure in a 'pipe 32 leading tothe feed control valve l6. Connected to the A chamber of relay 3| is apipe 33 in which is an air loading pressure established by a pilot valve34 positioned by the water level measuring controller 35. Thus thechamber A of relay 3| is continually subjected to a loading pressurerepresentative of water level while the B chamber is subjected to thecontrol pressure established by relay 22. The resulting operation isthat relay 3| will come to a balance condition when the actual Waterlevel is such that the rate of steam generation satisfies the demand andsteam pressure is at the desired value. If steam pressure departs ineither direction beyond predetermined limits the water level controllerwill have full control since the slightest unbalance in relay 3| will beable to obtain full movement of the feed valve IS in either direction.

Interposed in the pipe 32 we provide a selector valve 36 similar to thetype disclosed and claimed in the patent to Fitch 2,202,485; thusproviding a possibility for remote manual or automatic selective controlof the valve l6.

In order to maintain uniform concentration of dissolved solids in theboiler, and thereby a uniform value of water conductivity, a continuousbleed system is provided. In the bleed line l5 we indicate a controlvalve 31 actuated conjointly responsive to water level within the drum land to rate of steam outflow. Primarily the rate of bleed should beproportioned to the rate of steam outflow for that is the rate at whichthe concentration of the boiler water is increasing. However, for agiven water level in the boiler drum, there should be a given steam flowproduced. If there is a greater or lesser amount of steam outflow thanthat theoretically produced for a given water level in the drum it isdue in part at least to a greater or lesser concentration of dissolvedsolids in the boiler water which of course varies pacity of the waterbetween the electrodes. Some effect will of course be had by variationin temperature of the water within the boiler drum. 5 Therefore, bycontrolling the bleed valve 31 both from water level and from steam flowthe correctconcentration of dissolved solids should be maintained in theboiler drum.

At 38 we indicate a measuring controller sensiduit l1. Controller 38positions the movable element of a pilot valve 39 to establish in thepipe 40 a loading pressure representative of rate of steam outflow. Thepipe 43 is connected to the 4| loading pressure within the relay 4|pressure representative of steam outflow rate a pipe 33A. Thus withinlevel, to establish a resultant control pressure in the pipe 42 forpositioning the bleed valve 31. Interposed in the pipe 42 is a selectorvalve 43 control of the valve 31.

It will be observed that eifect is applied to the B while the steam flow(SF) effect is applied to the A chamber. From a balance condition; anincrease in pressure in the A chamber so positions the valves of the Dchamber as to increase the pressure therein, resulting in a positioningof valve 31 in an opening direction. On the other hand, an increase inpressure in the B chamber results in a closing movement of valve 31.

Assume a steady load condition with water level corresponding to steamoutflow, steam pressure as desired, and tioned to output rate.

An increase in steam demand occurs. Steam flow increases and steampressure drops. Feed water rate is increase (relay 3 to raise the level,thus increasing the electrode immersion, and increase the current path.Pressure within the A chamber of relay 4| increases immediately andbefore any change in pressure in the B chamber (from WL) can occur. Thisresults in an increase of pressure within the D chamber and consequentlyan opening motion of bleed valve 31. Subsequently, as the rate of feedis increased (by relay 3|) the rising water level will result in anincrease in pressure in the B chamber of relay 4|. When the unitstabilizes at the new rate of vapor outflow, water level and feed ratecorresponding thereto, and optimum steam pressure; the relay 4| willhave come to a balance condition with the bleed rate properlyproportflioned to the new conditions of inflow and outow.

On the other hand, should steam demand decrease, steam pressure willrise, feed input rate will decrease, pressure within chamber A of relay4| will decrease, and bleed valve 31 will move in a closing direction.

Thus it will be seen that the bleed rate is proportioned to the vaporoutflow or load upon the unit and consequently to the rate of supply offeed water; with a continual check-back from level within the boiler.

In addition to the high and low water level limits, described inconnection with the relay 22, we provide an emergency blowdown systemincluding a blowdown valve 44 interposed in the blowdown pipe I4 andunder control of steam 75 pressure through the agency of a relay 45. The

the water level (WL) chamber of relay 4|,

the current carrying cit-- tive to the rate of steam outflow through thecon-' A chamber of a difierential standardizing relay' to the B chamberof which is applied the we continually compare a loading with a loadingpressure representative of waterproviding the possibility of hand orautomatic bleed rate properly propor-- -'There is, of course, a

7 relay 45 assists the steam pressure controller in maintaining steampressure within desired limits on a. sudden decrease in steam demand.Normally the bloWdown valve 44 is closed. Should a sudden decrease insteam outflow occur it may not be possible for the water level in theboiler to be immediately evaporated down to that value corresponding tothe required steam output of the boiler, through closing down the feedwater valve I under the dictates of the rising steam pressures and waterlevel. The steam pressure would then increase beyond the standard andthe master loading pressure in pipe 2| would also increase above thestandard value. When increased sufiiciently above standard, dependingupon the adjustment of relay 45, the blowdown valve 44 will start toopen up so as to assist in dropping the level of water in the boilerdrum, and thus decrease the rate of steam generation so as to bring thesteam pressure back to the normal value.

The loading pressure within the pipe 2| is applied to both the A and Cchambers of the relay 45 while the opposing chamber B is left open tothe atmosphere. Thus the loading pressure is doubly eifiective inpositioning the supply and bleed valves of chamber D of the relay. Theinitial spring loading adjustment of the relay is such that the pressurewithin the pipe 2| is not effective in positioning the valves of therelay 45 until after a predetermined high loading pressure is attained,representative of a predetermined high steam pressure acting on theBourdon tube I8.

Thus it is seen that the blowdown valve 44 is normally closed and isopened only under what may be termed an emergency condition of highsteam pressure when it is desired to more rapidly relieve water from theboiler drum than is possible by merely shutting off the supply line l2and l waiting for the level to be lowered through evaporation of thatwater which is still in the boiler.

Interposed in the pipe 4! is a selector valve 46 which joins the Dchamber of relay 45 to the blowdown control valve 44 and allows thepossibility of hand or automatic control of the latter. In order thatthe boiler may be blown down manually we provide a manually operablevalve 48 bypassed around the control valve 44.

In general, the control system of Fig. 1 provides that the greater thedepth of submersion the greater the contact area of the boiler waterwith the heating units becomes and consequently the greater the steamingrate of the unit will be. desirable maximum and minimum level of waterin the boiler not to be exceeded.

The steam pressure controller has two principal functions:

1. To control or maintain water level in the boiler to maintain steampressure within de sired limits at different loads.

2. To open the blowdown valve in the event that the steam pressureincreases. beyond a predetermined high value. Blowdown valve 44 isnormally closed and opens only upon emergency high pressure. Forinstance, the doubling relay 45 is so adjusted that for an increase ofsay 25-35 p. s. i. loading pressure from pilot 20 the output of therelay will cover the range of 5-25 p. s. i. for opening valve 44.

The water level controller 35 functions to simultaneously open both thefeed water valve and the bleed valve 31 as rating (steam flow) increasesand subsequently, as the operating water level in the generator isincreased. Although called a water level controller its essentialfunction serves primarily to maintain an increase in rate of fresh feedwater flow as boiler demand increases and also to stabilize the actionof the steam pressure controller in the operation of the feed watervalve.

Water concentration is controlled from two variables, namely, waterlevel and steam flow. These two variables open the bleed valve and alsothe feed valve with an increase in unit output to maintain concentrationWithin the desired operating limits.

In Fig. 2 we show diagrammatically a modification of the arrangement ofFig. 1 and which is adapted more particularly to rapidly fluctuatingload demands upon the unit. In Fig. 2 we have used the same referencenumerals for elements which are identical with those previouslydescribed in connection with Fig. 1. On both of these drawings thearrows on the various control pipes indicate the direction ofapplication of loading pressure, 1. e. from a controller to a relay orfrom a relay to a controlled valve.

In the arrangement of Fig. 2, we again indicate a control of the feedinlet valve I6 from a measure of steam pressure modified by anindication of level of water within the boiler drum. Additionally, thevalve 16 is under the control of a comparison of steam outflow rate withwater inflow rate.

For comparing the rate of steam outflow with the rate of water inflow,we show the steam flow controller 38 and a water flow controller 49adapted to position a comparing linkage 50 for positioning a pilot valve5!. The usual adjustments are provided in the individual flowcontrollers so that desired proportionality may be established betweenthe two rates of flow. The and signs adjacent the linkage 50 indicatethe direction of motion of the controller arms of the steam flow meterand of the water flow meter for an increase or a decrease in rate offlow. When desired proportionality between the rate of vapor outflow andthe rate of water supply is attained, the linkage 50 will be in such aposition (regardless of the actual value of the rates) that the pilot 5]will establish a predetermined loading pressure within a pipe connection52. Should the interrelation between steam flowv and water flow departfrom desired proportionality the loading pressure within the pipe 52will be greater or lesser than the predetermined value.

The loading pressure within the pipe 52 is imposed upon the A chamber ofa differential or comparison and standardizing relay 53 whose outputfrom the D chamber, is applied to the pipe 54 and therefrom imposed uponthe valve 16 for positioning the same. To the B chamber of the relay 53we apply a loading pressure, through the pipe 55, originating in the Dchamber of a relay 55 which is a comparison relay for comparingpressures representative of steam pressure and water level.

The steam pressure pilot valve 20 establishes in the pipe 2! a pressurerepresentative of steam pressure and applies the same to the A chamberof a standardizing relay 51. To the A chamber of the relay 56 we applythe output pressure from the relay 51, while to the B chamber of relay56 is applied (through the pipe 58) a pressure established by the waterlevel pilot valve 34. Thus it will be seen that the relay 56 establishesa loading pressure in the pipe 55 representative of demand upon thevapor generator as indicated by steam pressure and modifies this effeetby a pressure representative of the actual level of water within theboiler drum.

In the present embodiment, the rate of supply of water to the boilerdrum is adjusted under the dictates of four variables in the operationof the unit. Under any steady load condition it is apparent that therate of liquid inflow to the boiler should equal the rate of vaporoutflow plus any bleed. There will be little effect upon the valve Hifrom the steam pressure controller or from the water level controllerinasmuch as under such steady load conditions these variables should notbe fluctuating. However, should any of the Variables tend to fluctuate,they will impose a correction upon the loading pressure within the pipe54 and correspondingly correct the rate of water input to the boiler.

The steam flow controller and the water flow controller are eachdesigned on a weight rate basis for proper comparison. Should there be adeviation in steam pressure, steam temperature, or feed water pressure,one or the other of these flow controllers may give a slightly incorrectrepresentation of true weight rate. Thus, the comparison between the twomight indicate a proper proportionality between weight rate of liquidinflow and weight rate of vapor outflow whereas actually theproportionwould not be exactly correct. With the check back however fromactual water level such discrepancy will be corrected. At the same timethe modified control from steam pressure will be efiective to take careof minor departures in steam pressure from the desired value. I

When a change in load (for example an increase in steam demand) occurs,this will show up in an increase of the steam flow and a correspondingdecrease in steam pressure. As previously mentioned, the desiredoperation is to raise the water level on the electrodes to increase therate of steam generation. The increased steam flow and the decreasedsteam pressure will act in the same direction to demand an increase inrate of feed water until the comparison between steam outflow rate andfeed water input rate attains desired proportionality. If the waterlevel has not reached the proper value to satisfy the new demand, thewater level controller will impose its control upon the feed water valveIt. In general, the four variables, namely, steam outflow, water inflow,steam pressure, and water level will coact to properly position the feedinput ..valve [6 to satisfy the steam demand upon the unit andmaintainsteam pressure substantially uniform. It will be appreciated that thevarious control instrumentalities, such as regulators, re-

lays, pilot valves, etc, may be adjusted for sensitivity, range, limits,etc. Inasmuch as such adjustments are known, it does not appear to benecessary to go into the details thereof.

Fig. 2 shows a control of the bleed valve 31 conjointly from steamoutflow, steam pressure and water level. A loading pressurerepresentative of each of these three variables is algebraically addedin a relay 59 from which a resultant control pressure is applied,through the pipe 42 and selector valve 43, to positon the valve 31.

It will be observed that in this arrangement the steam flow efiect isapplied to the A chamber of relay 59, the water level effect to the Bchamber and the steam-pressure effect to the C chamber. Under relativelysteady load conditions the steam flow effect and water level efiectofiset each other so that the steam pressure variations substantiallycontrol the positioning of the bleed valve Bl, one way or another from athrottled condition corresponding to the basic steam flowwater leveldictates (load demand upon the unit).

Assuming, from a steady state condition, an

increase in steam outflow with resulting decrease in steam pressure.Pressure within the A chamber increases while pressure within the Cchamber decreases. The tendency is to offset each other so that noresultant positioning of the valve 31 occurs. No immediate change hasoccurred in water level so that the pressure in chamber B remains asbefore. Thus there is no immediate change of the rate of bleed in eitherdirection.

As the increased rate of feed to the boiler results in an increase inwater level the pressure within the B chamber increases, tending tocounteract the increased pressure in the A chamber with the result thatthe C chamber pressure becomes more effective in positioning the valve31. Inasmuch as the decreasing steam pressure lowered the pressure inthe C chamber then the positioning of the valve 31 will be in a closingdirection as water level is increased. Thisis proper to offset thedilution and lowering of temperature caused by the increased rate offeed increased volume of water within the drum.

Following this action, as steam pressure rises, it opens the bleed dueto an increase in pressure within the C chamber, until, when a steadystate of operation is reached, the steam flow effect within the Achamber balances the water level effect within the B chamber and anyvariation in steam presssure effect within the C chamber controls thebleed valve; from a new opening condition representative of the newvapor outflow rate and corresponding water level.

It may be said, in general, that the arrangement of Fig. 2 for bleedvalve control normally balances an effect from steam flow against aneffect from water level and utilizes variations in steam pressure eflectto continuously readjust the position of the bleed valve. The valve isunder the conjoint control of the three variables whose effects arealgebraically added within the relay 59.

As in Fig. 1, the control of the blowdown valve 44 is from the steampressure pilot 20 acting through a doubling relay 45.

In Fig. 3 we illustrate a modification of Fig. 2. Herein we have showndiagrammatically the control of the feed water input valve l5 conjointly55 from the four variables steam pressure, steam flow, water level andwater flow. In this illustration we have not shown, evendiagrammatically, the boiler nor the control of blowdown or of the bleedvalve which may be as described in no connection with Fig. 1 or Fig. 2.The arrangement of Fig. 3 depicts a modification in the control of thefeed water inflow valve, particularly useful under certain operatingconditions. It may be said that in Fig. 3 an air loading pressure is 65established within the pipe 2| representative of steam pressure, an airloading pressure within the pipe 40 representative of weight rate ofsteam outflow, an air loading pressure within the pipe 58 representativeof water level within the boiler 70 drum, while an air loading pressureis established in the pipe 6| representative of weight rate of waterfeeding the boiler.

We apply the steam flow effect to the A chamber of a relay 62, to the Bchamber of which we 75 apply the steam pressure efiect. Connected to theinlet and outlet valves of the relay 62 are load limiting relays 63, 64performing the function of the elements 24, 25, 2B and 29 of Fig. 1.Thus the resultant effect, from the D chamber of the relay 62, asapplied through the pipe 65, has a maximum and a minimum limitestablished by the adjustment of the relays 63 and 64.

The loading pressure resultant of steam pressure and steam flow,available in the pipe 65, is applied to the A chamber of a relay 66 forcom- ;parison with the water level effect available within the B chamberfrom the pipe 58. The output of the relay 66, available through the pipe61, is applied to the A chamber of a standardizing relay 68, to the Bchamber of which We apply the water flow effect through the pipe 6!. Theoutput of the relay 68 is available in a pipe 54 for positioning thefeed valve Hi.

It will be evident from a study of Fig. 3 that the differential relay 62continually interrelates pressures individually representative of thetwo operation variables first to show the eifect of changes in demandupon the boiler, namely, steam pressure and steam outflow rate. Eitheror both of these operation variables may change, but normally they varyin opposite direction, i. e. an increase in steam outfiow rate is accompanied by a decrease in steam pressure, and vice versa. Thus upon anincrease in steam outflow the pressure within the A chamber of relay 8?will increase while the pressure within the B chamber will decrease.These effects are additive to increase the loading pressure output ofthe relay 62 through pipe 65 to the A chamber of relay 66, resulting inan increase in pressure within chamber A of relay 68 and in an openingof the feed valve Hi.

The resultant efi'ect of steam flow and steam pressure (in chamber A ofrelay E6) is modified in accordance with water level as imposed upon theB chamber. Likewise the pressure efiect in the A chamber of relay 68 ismodified by a pressure in the B chamber representative of Water flowrate. Thus when the valve 16 is positioned to satisfy the dictates ofsteam pressure, steam flow and water level it should result in a rate offeed water admission to the boiler such as to satisfy said threevariables. As a check upon the actual rate of water flow the water flowmeter 49 establishes a loading pressure representative of water flowrate within the B chamber of the relay B8 and compares this against theeffect established within the chamber A. If the proper rate of wateradmission is not attained due, perhaps, to fluctuations in feed waterpressure, then the positioning of the valve i6 is modified responsive tothe interrelation between the pressure effects within the chambers A andB of relay 68.

While we have chosen to illustrate and describe certain preferredembodiments of our invention, it will be understood that this is by wayof explanation only and is not to be considered as limiting.

What we claim as new, and desire to secure by Letters Patent of theUnited States, is:

1. The method of operating a steam generator of the type whereinelectric energy is dissipated in the water of the generator forvaporizing the water, which includes, continuously establishing acontrol effect representative of the pressure of the vapor generated,continuously establishing a control effect representative of the levelof water within the generator and consequently of the area of the liquidpath to be traversed by the elec- 12 tric current, and utilizing the twocontrol effects conjointly to control the rate of supply of water to thegenerator.

2. The method of claim 1 wherein each of the control effects is a fluidpressure.

3. The method of claim 1 including the further step of continuouslyestablishing a control effect representative of the rate of steamgeneration, and including this latter control effect in the conjointcontrol of the rate of supply of water to the generator.

4. The method of claim 1 including the further steps of continuouslyestablishing a control effect representative of the rate of steamgeneration, continuously establishing a fourth control effectrepresentative of the rate of feed water supply to the generator, andinterrelating the four control effects to control the rate of supply offeed water.

5. The method of controlling the operation of an electric steamgenerator which includes, feeding the unit with water to form a pool inwhich the electrodes are immersed for vaporizing the water, determiningthe extent of immersion, obtaining a representation of the steam demandupon the unit, and continuously utilizing the values of these twovariables in controlling the rate of feeding of water to the generator.

6. The method of claim 5 wherein the steam demand upon the unit is therate of flow of steam discharged from the unit, and so controlling therate of water supply to the unit that a predetermined relation willexist between submergence of the electrodes and rate of steam outflow.

'7. The method of claim 5 wherein the steam demand is represented bypressure within the generator, and rapidly blowing down or dischargingwater from the pool to decrease electrode immersion when steam pressureexceeds a predetermined value.

' '8'. The method of controlling the operation of an electric steamgenerator which includes, feeding the unit with water to form a pool inwhich i the electrodes are variably immersed for vaporizing the water,determining the extent of immersion, determining the rate of steamoutflow from the generator, determining the pressure within thegenerator, continuously controlling the rate of feed of water to theunit in response to the extent of immersion and the steam pressure,bleed ing water from the pool at a rate dependent upon the rate of steamoutflow to control the conductivity of the water in the pool, andrapidly blowing down or discharging water from the pool to decreaseelectrode immersion when steam pressure exceeds a predetermined value.

9. The method of claim 8 including the step of limiting the immersion ofthe electrodes between predetennined high and low limits.

10. The method of controlling an electric steam generator supplied withliquid under pressure and having provision for bleeding liquid from thegenerator at a controllable rate for regulatin the conductivity of thewater within the generator, which includes, continuously developing acontrol effect representative of load demand upon the unit, andutilizing the control effect in establishing the rate of bleed.

11. The method of controlling an electric steam generator supplied withliquid under pressure and having provision for bleeding liquid from thegenerator at a controllable rate for regulating the conductivity of thewater within the generator,

which includes, controlling the rate of bleed 13 responsive to departureof desired interrelation between rate of steam outflow and liquid levelin the generator, and modifying such control in response to steampressure.

12. The method of controlling an electric steam generator supplied withliquid under pressure for variably immersing the heating electrodes,which includes, separately obtaining effects representative of steampressure, rate of steam outflow, rate of water inflow and liquid levelrelative to the electrodes; and continuously regulating the rate ofsupply of liquid to the generator conjointly responsive to such effects.

13. The method of claim 12 including the further step of firstproportionately comparing the rate of water inflow to the 'rate of steamoutflow and then utilizing any discrepancy from desired porportionalityin modifying the control of liquid feed from both steam pressure andwater level.

14. The method of claim 12 including the further step of bleeding waterfrom the generator at a rate controlled conjointly responsive to steampressure, rate of steam outflow and water level.

15. The method of controlling an electric steam generator supplied withliquid under pressure for variably immersin the heating electrodes,which includes, continuously producing a control eflect conjointlyrepresentative of steam pressure and steam outflow rate, as anindication of load demand upon the generator, modifying the controleffect upon departure of water level from that which is dictated by loaddemand, controlling the rate of liquid supply by the modified controleffect, and continuously checking back from the actual rate of liquidsupply to see if it is as dictated by the modified control effect.

16. The method of controlling an electric steam generator supplied withliquid under pressure for variably immersing the heating electrodes,which includes, controllably bleeding water from the generator formaintaining substantially constant the conductivity of the water bytemporarily varying the rate of bleed in opposite sense to a change inrate of steam outflow, followed by a proportioning of the rate of bleedto the rate of steam outflow.

17. The method of controlling an electric steam generator supplied withliquid under pressure for variably immersing the heating electrodes,which includes, normally maintaining a liquid level varying with demandupon the unit, feeding water to the unit in proportion to steam outflow,and. controlling a bleed of water from the unit directly proportional tosteam outflow rate and to water level and inversely proportional tosteam pressure so as to maintain conductivity substantially uniform.

18. In combination with an electric steam generator having provisionsfor supplying feed water thereto, means sensitive to water level withinthe generator, means sensitive to steam pressure within the generator,and a single control valve regulating the rate of supply of feed waterand adapted to be positioned through the coactive agency of said means.

19. In combination with an electric steam generator having provisionsfor supplying feed water thereto, means establishinga fluid controlpressure representative of steam pressure within the generator, meansestablishing a fluid control pressure representative of Water levelwithin the generator, and a single means continuously responsive to saidtwo fluid pressures adapted to control the rate of feed water supply.

20. The combination of claim 19 including means establishing a thirdfluid control pressure representative of the rate of steam outflow, saidmeans which controls the rate of feed water supply being continuouslyresponsive to all three fluid control pressures.

21. The combination of claim 19 including means establishing a thirdfluid control pressure representative of the rate of steam outflow, andmeans establishing a fourth fluid control pressure representative of therate of Water inflow, said means which controls the rate of feed watersupply being continuously responsive to all four fluid controlpressures.

22. Apparatus for controlling the operation of an electric steamgenerator including in combination, means continuously producing acontrol effect representative of demand upon the generator, meanscontinuously producing a control effect representative of water level,and control means continuously regulating the rate of supply of water tothe generator responsive to the two mentioned control effects.

23. The apparatus of claim 22 wherein the control effects are fluidpressures.

24. The apparatus of claim 22 including means continuously producing acontrol effect representative of the rate of steam generation, saidthree control effects arranged to conjointly actuate the said controlmeans.

25. In combination with an electric steam generator having provisionsfor supplying feed water thereto, means determining the rate of steamoutflow from the generator, means determining the level of water withinthe generator, and control means responsive to said two determiningmeans and adapted to so control the rate of feed water supply that apredetermined relation will exist between the rate of steam outflow andthe amount of submergence of the electrodes.

26. In combination with an electric steam generator having provisionsfor supplying water thereto to form a pool in which the electrodes arevariably immersed for vaporizing the water, i."- means establishing afluid control pressure representative of steam pressure within thegenerator, means establishing a fluid control pressure representative ofwater level within the generator, control means adapted to regulate therate of supply of water responsive to both said fluid control pressures,and means arranged to rapidly discharge water from the generator whensteam pressure exceeds a pretermined value.

2'7. In combination with an electric steam generator having meanssupplying water thereto to form a pool in which the electrodes arevariably immersed for vaporizing the water, a flrstmeans determining theextent of immersion, second means determining the rate of steam outflow00 from the generator, third means determining the pressure of the steamgenerated, means continuously controlling the rate of supply of water tothe unit in response to the first means and the third means, meansbleeding water from the pool 66 at a rate dictated by the second namedmeans to control the conductivity of the water in the pool, and blowdownmeans arranged to rapidly discharge waterfrom the pool when the thirdmeans determines an excessive steam pressure.

28. The combination of claim 27 including means limiting the immersionof the electrodes between predetermined high and low limits.

29. Apparatus for controlling an electric steam generator having meanssupplying water thereto 75 to form a pool in which the electrodes arevariably immersed for vaporizing the water, which includes incombination, a controller for the water supply means, a liquid levelresponsive device arranged to normally actuate the controller inaccordance with liquid level within the generator, and pressureresponsive means subjected to the pressure of the generated vapor andadapted to modify the actuation of the controller by the levelresponsive device.

30. Apparatus for controlling an electric steam generator having meanssupplying water thereto to form a pool in which the electrodes arevariably immersed for vaporizing the water and having means for bleedingwater from the pool at a controllable rate for regulating theconductivity of the water in the pool, which includes in combination,means sensitive to rate of steam outflow from the generator, and meanspositioned by said sensitive means controlling the bleeding means.

31. Apparatus for controlling an electric steam generator having meanssupplying water thereto to form a pool in which the electrodes arevariably immersed for vaporizing the Water and having means for bleedingwater from the pool at a controllable rate for regulating theconductivity of the Water in the pool, which includes in com- 'bination,means sensitive to rate of steam outflow 'from the generator, meanssensitive to the extent of immersion of the electrodes, comparison meansresponsive to said two sensitive means continuously determining theinterrelation between rate of steam outflow and immersion of the heatingelectrodes, said comparison means adapted to regulate the bleedingmeans, and means sensitive topressure within the generator arranged tomodifylthe effect of the comparison means upon the bleeding means.

32. Apparatus for controlling an electric steam generator supplied withwater under pressure for variably immersing the heating electrodes,which includes in combination, a plurality of means separately sensitiveto steam pressure, to rate of steam outflow, to rate of water inflow andto liquid level relative to the electrodes; and means continuouslyregulating the rate of liquid supply conjointly responsive to saidplurality of sensitive means.

' 33. The combination of claim 32 including means for bleeding waterfrom the generator, and control means for positioning said bleedingmeans 'conjointly responsive to the steam pressure, rate of steamoutflow and water level sensitive means. 34. Apparatus for controllingan electric steam generator supplied with water under pressure forvariably immersing the heating electrodes, which includes incombination, means continuously produ'c'ing a control effect conjointlyrepresentative of'steam pressure and steam outflow rate, as anindication of load demand upon the generator,

means sensitive to water level within the generator continuouslymodifying said control effect Cir generator supplied with water underpressure to form a pool of water in the generator in which theelectrodes are variably immersed for vaporizing the water and havingmeans for bleeding water from the pool at a controllable rate forregulating the conductivity of the water in the pool, which includes incombination, control means for regulating the rate of bleed from thepool, and means sensitive to the rate of steam outflow from thegenerator for positioning the control means, the rate sensitive means soarranged that upon change in rate of steam outflow the control of bleedwill first be in opposite sense to the change in rate of steam outflowfollowed by a positioning of the bleed control means in the same senseas the change in rate of steam outflow.

37. The method of controlling an electric steam generator supplied withliquid under pressure and having provision for bleeding liquid from thegenerator at a controllable rate for regulating the conductivity of thewater within the generator, which includes, continuously developing acontrol efiect representative of rate of steam outflow from the unit,and utilizing the control effect in establishing the rate of bleed.

38. The method of operating a vapor generator of the type whereinelectric energy is dissipated in the liquid of the generator forvaporizing the liquid, which includes, continuously establishing a firstpneumatic control pressure varying in value with the pressure of thevapor generated, continuously establishing a second pneumatic controlpressure varying in value with the level of liquid within the generatorand consequently with the area of the liquid path to be traversed by theelectric current, and continuously regulating the rate of supply ofliquid to the generator conjointly responsive to both the pneumaticcontrol pressures.

CHARLES F. BIRCHLER, HARRY E. WEAVER.

REFERENCES CITED UNITED STATES PATENTS Name Date Eaton Mar. 28, 1933Number

